This application claims the benefit of Japanese Patent Application P2001-352964, filed on Nov. 19, 2001, the entirety of which is incorporated by reference.
The present invention relates to ceramic heaters, a process for producing the same, and heating apparatuses for a semiconductor producing system.
In a semiconductor producing system, a ceramic heater has been provided for heating a wafer (substrate) so as to deposit a semiconductor thin film on the wafer from gaseous raw materials such as silane gas by means of thermal CVD or the like. In such a heater, it is necessary to maintain a high temperature on a heating face and to assure the temperature uniformity on the heating face so as to prevent semiconductor defects. Such a ceramic heater, however, is generally made of a ceramic substrate and a heat generator embedded in the substrate, so that some degree of temperature difference may be observed on the heating face.
Japanese patent publication 6-53, 145 A discloses a technique for improving the temperature uniformity on the semiconductor heating face of a ceramic heater. That is, a disk-shaped ceramic heater with a heating face for a heating semiconductor is produced. The temperature distribution on the heating face is then observed with a thermograph. The thus observed temperature distribution is then subjected to image processing to obtain image-processed data. A reflector is provided on a position opposing the back face of the ceramic heater. The heat that is radiated from the back face of the ceramic heater is reflected by the reflector and irradiated into the heater again. The temperature distribution of the reflector is controlled based on the image-processed data. In the region where a lower temperature is observed on the heating face, the thermal absorptance of the reflector is reduced, so that the heat reflected by the reflector into the heater may be increased. The temperature in the region with the lower temperature observed may be thus increased. The surface of the reflector is subjected to sandblasting to control the surface roughness and thus to control the reflectance of the reflector.
The inventor has studied the above technique in Japanese patent publication 6-53, 145 A and encountered the following problems. That is, it is necessary to fix a reflector in a specific position opposing the back surface of the ceramic heater in the semiconductor chamber. After fixing the reflector, the distribution of the thermal absorptance (or thermal reflectance) on the reflecting face of the reflector should be accurately matched with the temperature distribution on the heating face of the ceramic heater before fixing the reflector. It is difficult, however, to adjust the positions of the heating face of the heater and of the reflecting face of the reflector for the following reasons:
(1) The center of a circular heating face of the ceramic heater should be accurately matched with the center of the circular reflecting face of the reflector; and
(2) In addition to this, the angle and diameter of each position of the heating face with respect to the center should be accurately matched with those of each position of the reflecting face with respect to the center.
Furthermore, even if such a two dimensional position adjustment is successfully performed, such an adjustment is insufficient for obtaining temperature uniformity on the heating face within specification for the following reasons. That is, the distance between the back face of the heater and the reflecting face of the reflector is also important. Specifically, the thermal absorptance of each point on the reflecting face is calculated and designed on the provision that a distance between the reflecting face and the back face of the heater is a specific value xe2x80x9cxcex1.xe2x80x9d When the distance between the reflecting face and back face is smaller than xe2x80x9cxcex1,xe2x80x9d heat transmitted from the reflecting face to the back face of the heater is increased so that the temperature on the heating face of the heater may be increased. The following adjustments (3) and (4) are thus needed:
(3) the distance between the back face of the heater and the reflecting face of the reflector must be controlled to a specific value xe2x80x9cxcex1;xe2x80x9d and
(4) the back face of the heater and the reflecting face must be parallel with each other over the whole of the back face.
It is difficult to set and fix the reflector in a semiconductor chamber while maintaining the above four geometrical conditions. Furthermore, the fixed reflector may result in a complicated structure, and the reflector may be deteriorated, fractured or warped due to thermal stress which produces adverse effects on the gas flow.
An object of the present invention is to provide a novel ceramic heater having a ceramic substrate with a heating face and a heat generator so that the temperature on the heating face may be controlled without the necessity of a temperature controlling member that is separate from the substrate.
The present invention provides a ceramic heater having a heat generator and a ceramic substrate with a surface including a heating face. A first region is provided on the surface and out of the heating face, and a second region is provided on the surface and out of the heating face. The second region has a lower emissivity of thermal radiation than that of the first region.
The present invention further provides a heating apparatus for a system for producing semiconductors. The heating apparatus includes a ceramic heater with a back face, a terminal connected with a generator, a hollow supporting member defining an inner space and fixed on the back face of the heater, and a power supply means provided in the inner space and electrically connected with the terminal.
A semiconductor producing system means a system usable in a wide variety of semiconductor processes in which metal contamination of a semiconductor is to be avoided. Such a system includes film forming, etching, cleaning and testing systems.
The present invention also provides a method for producing a ceramic heater having a heat generator and a ceramic substrate with a surface including a heating face. The method includes the step of providing a first region and a second region both on the surface and out of the heating face. The second region has a lower emissivity of thermal radiation than that of the first region.
The inventor has tried to divide the surface of the ceramic substrate itself, other than the heating face, into a plurality of regions having the different thermal emissivities with respect to each other. The inventor has thus studied the effects on the heating face of the substrate. As a result, the inventor has found that the temperature uniformity on the heating face may be substantially affected beyond expectation. The present invention is based on these findings.
For example, when a cold spot is observed on a heating face of a ceramic substrate, the emissivity of thermal radiation may be reduced in a projected area defined by projecting a planar pattern of the cold spot onto the back face. It is thereby possible to slightly increase the temperature in the cold spot on the heating face so that the cold spot may be cancelled. Alternatively, when a hot spot is observed on a heating face of a ceramic substrate, the emissivity of thermal radiation may be increased in a projected area defined by projecting a planar pattern of the hot spot onto the back face. It is thereby possible to slightly reduce the temperature in the hot spot on the heating face so that the hot spot may be cancelled. Such changes or control of the emissivity of thermal radiation of a part of the surface of the ceramic substrate may be performed only with surface processing of the ceramic surface. It has not been known that the temperature distribution on the heating face may be considerably improved only by performing surface processing of the ceramic substrate to control the emissivity of thermal radiation.
These and other objects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art.